Transplantation offers the promise of life saving and health restoring therapy for hundreds of thousands of patients suffering from end-stage organ failure. Outstanding short-term outcomes have been achieved through the development of multi-drug life-long continuous immunosuppressive regimens. Despite these achievements, significant challenges remain that compromise long-term outcomes and limit the application of transplantation. Premature graft loss and death remain as stubborn adversaries as evidenced by the inexorable and stagnant graft and patient annual attrition rates that plague our patients. Until recently, virtually all transplant regimens relied on calcineurin-inhibitors as their cornerstone immunosuppressive agent. The approval of belatacept, a second generation CD28 pathway inhibitor provides an alternative that addresses some of the limitations inherent in CNI-based immunosuppression and provides a long-awaited tool in the quest for transplantation tolerance. Belatacept avoids CNI-induced nephrotoxicity, is associated with very low de novo DSA rates, and improves the CV risk profile. Unfortunately, barriers to wide-scale application and improving long-term results persist. As foreshadowed by our early studies in mice and NHP identifying costimulation blockade-resistant rejection, the rates and grades of acute cellular rejection are higher with belatacept than CNI. Importantly, we have recently identified a memory T cell biomarker that correlated with increased risk of costimulation blockade-resistant rejection (CoBRR) in both NHP and humans. The use of this predictive biomarker may allow us to identify optimal candidates for costimulation-blockade-based tolerance induction therapies. Further, exploration of critical pathways utilized by costimulation-independent memory T cells, and development of next-generation cellular therapies including optimized eTreg, bone marrow products, and mesenchymal stromal cells (MSCs) will provide powerful strategies to mitigate risk of rejection and promote tolerance induction in recipients in which the risk of rejection is high. The development of tolerance induction protocols based on the immune status of individual recipients will facilitate personalized strategies for tolerance induction, to minimize peri-transplant immunosuppression and preserve protective immunity. Thus, the central goal of our research program and this application is to develop clinically applicable approaches to address near-term needs and ultimately to develop broadly applicable tolerance strategies for use in clinical transplantation, with the underlying theme that the same strategy may not be optimal for every recipient. This goal will be accomplished via two interrelated projects and a supporting scientific core.